1. Field of the Invention
The present invention relates to a device for coupling two rotary machines which provides for automatic uncoupling under certain conditions.
2. Summary of the Prior Art
As is known, dependent upon operational phases of two rotary machines, in certain applications, the transmission of motion may take place either in a first sense, or in an opposed sense to the first which will be referred to as the second sense of motion transmission. A torque level which is substantially different may thus be exerted in each sense. It will be assumed as a consequence that the first selected sense of transmission of motion corresponds to a higher torque level and the second sense to a lower torque level. These operational conditions, for example, will apply particularly where one of the rotary machines is a turbo-machine starter and the other rotary machine is the auxiliaries gearbox of the said turbo-machine utilized for driving various auxiliaries through several kinematic chains. During the starting of the turbo-machine, the starter drives at least one rotary body of the turbo-machine through the intermediary of the auxiliaries gearbox and in this first phase a substantial torque is transmitted through the line of transmission shafts. After normal running has been established, the turbo-machine drives the rotary parts of the auxiliaries gearbox and one shaft of the starter continues to be driven through its connection with the auxiliaries gearbox. In this second phase a torque is exerted which is obviously much lower than during the first phase as it is only required to drive the shaft of the starter without any opposing force, under normal operational conditions.
These results are obtained in known manner through power transmission means between the two rotary machines which are different in dependence upon the sense of motion transmission. For example, in the first sense of motion transmission where the torque level exerted is higher, this transmission is effected by a dog-clutch connection between a first and a second shaft. In the second sense of motion transmission opposed to the first sense this transmission is effected through an intermediate shaft of which each end is respectively disposed in the interior of a bore of the first shaft and a bore of the second shaft is rigid respectively with each of the first and second shafts, for example through a drive pin. In the two operational phases which apply in dependence upon the sense of motion transmission corresponding to the torque levels of a different order of value, it is necessary in order to avoid substantial damage or successive deteriorations in the parts in the drive train to protect the rotary machines in the eventuality of the accidental production in the power transmission line of an excess torque which may result from various originating causes which it is not possible to control entirely as a result of operational conditions imposed on the machines.
French Pat. No. A 1 521 603 describes several embodiments of torque-limiting devices employed in an engine kinematic chain comprising a plurality of motion transfers. A different torque limiter constituted by a hollow piece having a calibrated section of lower strength is integrated in this motion transfer chain. This known arrangement enables protection of several different units to which the motion is transmitted by a different train with limitation in the torque to a different level in accordance with the requirements of each chain. However, the proposed solution does not enable the protection of two rotary machines in which the transfer of motion can take place in the two senses with a torque level which is substantially different in each sense.
French Pat. No. A 2 094 274 relates to a bi-directional torque limiter in which a connection biased by a spring is provided between the driving and the driven elements and in which a member taking part in the transmission is adapted so as to be displaced on encountering the action of a spring in the case of an excess torque in order to engage with a fixed element. The embodiment described calls for the use of two ball systems for the transmission and this solution has been found inappropriate for certain uses and torque levels which it is proposed can be met by the present invention and it is similar for adjustment to different torque values which is proposed by the cited patent by giving an appropriate form to the seatings of the balls.
U.S. Pat. No. 2,964,931 describes an uncoupling device in which a shaft comprises a reduced section constituting a first torque limiter, this shaft is coupled to another shaft by a dog-clutch engaging in one sense of rotation and disengaging in the other sense and an intermediate connecting shaft also comprising a reduced section constituting a second torque limiter. The solution proposed by this patent enables uncoupling in the case of failure caused by torsion forces but does not permit uncoupling caused by alternating deflections created by radial forces acting on the shafts.
An object of the present invention is to overcome the disadvantages of previously known solutions.
A further object is to provide a device applicable particularly in the aeronautical field where rotary machines operate at very high rotational speeds, for example of the order of 20,000 r.p.m.